Tube for heat exchanger

ABSTRACT

In a tube ( 4 ) for a heat exchanger comprising a flat pipe ( 16 ) whose both ends are opened and in which a flow path ( 15 ) for a heat exchanging medium is formed, and an inner fin ( 17 ) arranged in the flow path ( 15 ), wherein said flat pipe ( 16 ) is constituted of a sheet of material for a flat pipe, the inner fin is constituted of two opposing flat plate portions ( 17   b   , 17   c ) connected along one of side edges of said flat pipe ( 16 ) and formed in a flat plate shape so as to be in contact with an inner surface of the said flat pipe ( 16 ), and projection portions ( 17   d ) which are projected from at least one of the flat plate portions ( 17   b   , 17   c ) and whose tops are in contact with the other opposing flat plate portion ( 17   b   , 17   c ). It is preferred that the projection portions ( 17   d ) are projected from both of the flat plate portions ( 17   b   , 17   c ) toward the opposing flat plate portion, and the opposing tops are made come in contact with each other. The tube for a heat exchanger which can prevent significant deformation of the inner fin from occurring when the inner fin included in the flat pipe is cut in a width direction thereof together with the flat pipe can be provided.

This application is a U.S. National Phase Application under 35 USC 371of International Application PCT/JP03/08018 filed on Jun. 25, 2003.

TECHNICAL FIELD

The present invention relates to tubes for a heat exchangercommunicating between tanks of the heat exchanger and allowing heatexchange medium to flow, and especially relates to tubes each of whichis formed by cutting a flat pipe and inner fin provided in the flat pipeat the forming of the flat pipe at the same time.

BACKGROUND ART

In recent air-conditioning units, it is considered to decreasevolumetric flow of coolant in a refrigerating cycle to design areduction of compressor's power as requirement for saving power and fuelefficiency. Thus, in a heat exchanger, it is desired to increase a heatexchanging efficiency so as to gain a heat exchanging ability more thanof the prior heat exchanger in a less volumetric flow of coolant. Underthus condition, though coolant distribution in the heat exchangerinfluences on the heat exchanging efficiency largely, it is difficult tofind an effective improvement plan for temperature distribution at thesmall volumetric flow due to the structure in a prior drawn cup typeheat exchanger in which a tank is provided only in one side thereof.Therefore, the heat exchanger is in course of shifting from one sidetank type of the heat exchanger to a both tank type heat exchanger whichhas tanks in both sides thereof these days.

Furthermore, there is a case that it is obliged to provide variousincidental equipments around an air conditioning unit. In thus case,because minimization of the air conditioning unit is required,minimization of the heat exchanger is more necessary with thisrequirement. Accordingly, it becomes more important problem to securethe heat exchanging ability more than in prior heat exchangers withsatisfying the requirement for minimization of the heat exchanger.

Though various improvements of the heat exchangers are considered fromthe above-mentioned point, above all, it is recognized as an effectivemeans to improve a tube structure. About the improvement of the tubestructure, it is desired to make an equivalent diameter of a flow pathsmaller as well as promoting flattening of the tube, and further it isconsidered as an effective means to provide inner fin in a flat pipe.

In the case of forming this tube, a flat pipe with a specific length isformed in advance and inner fin are inserted into the flat pipe andbrazed so far. However, according to this method, there is disadvantagethat productivity becomes worse because the inner fin must be insertedinto every flat pipe.

Accordingly, this applicant adopts a method for producing tubes by aroll forming in order to resolve the above disadvantage. This is that amaterial for a flat pipe is rolled up so as to cover the inner fin, aflat pipe A is formed while including the inner fin B in the flat pipeas shown in FIG. 10, and then a tube D with a specific length is formedby inserting a cutting blade C from one side in a width directionthereof to cut the flat pipe A together with the inner fin B.

However, because a shape of a prior tube is determined only in a viewpoint that the included inner fin makes an equivalent diameter of theflow path smaller, as shown in FIG. 10, there is a disadvantage that theinner fin B are deformed extremely and the flow path with smallequivalent diameter can not be formed because the inner fin B get out ofposition in an arrow direction illustrated with a broken line (a widthdirection of the tube) by the cutting blade C when the cutting blade Cinserted from the width direction in the case of forming the inner finin, for instance, a corrugated shape.

It is considered that this disadvantage is caused by that stiffness to awidth directional force of the inner fin itself, stiffness to a bindingforce by the flat pipe from a thickness direction thereof, and further acontact resistance to a width directional force at a contacting portionbetween the inner fin and the flat pipe are not secured because a shapeof the inner fin is determined only in a view point that the equivalentdiameter of the flow path is reduced.

Therefore, in this invention, it is a main object to provide tubes for aheat exchanger which can prevent much deformation of the inner fin tosecure a flow path with a small equivalent diameter in the flat pipe inthe case of cutting the inner fin included in the flat pipe togetherwith the flat pipe in the width direction.

More concretely, the object of the invention is to provide tubes for aheat exchanger so as to increase the stiffness to the width directionalforce of the inner fin itself and the stiffness to the binding force bythe flat pipe in the thickness direction thereof, and further to enlargethe contact resistance to a width directional force at a contactingportion between the inner fin and the flat pipe.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, a tube for a heat exchangeraccording to the present invention has a flat pipe whose both ends areopened and in which a flow path for a heat exchanging medium is formed,and an inner fin provided in the flow path of the flat pipe, and whichis constituted of a sheet of a material for a flat pipe, and ischaracterized in that the inner fin is constituted of two opposing flatplate portions connected along one of side edges of the flat pipe and isformed in a flat plate shape so as to be in contact with the innersurface of the flat pipe, and projection portions which project from atleast one of the flat plate portions and whose tops are in contact withthe other opposing flat plate portion.

Accordingly, because the inner fin including in the flat pipe is thattwo opposing flat plate portions are in contact with the inner surfacesof the flat pipe, it is possible to increase the stiffness to the widthdirectional force of the inner fin itself and the contact resistance tothe width directional force at the contact portion between the inner finand the flat pipe, and further because the projection portions incontact with the inner surface of the opposing flat plate are formed inat least one of the flat plates, it is possible to increase thestiffness to the binding force by the flat pipe in the thicknessdirection, as a result, it is possible to prevent the disadvantage suchthat significant deformation of the inner fin is occurred at the time ofcutting the flat pipe.

Besides, a tube for a heat exchanger according to the present inventionhas a flat pipe whose both ends are opened and in which a flow path fora heat exchanging medium is formed, and an inner fin provided in theflow path of the flat pipe, and which is constituted of a sheet of amaterial for a flat pipe, wherein the inner fin may be constituted oftwo opposing flat plate portions connected along one of side edges ofthe flat pipe and is formed in a flat plate shape so as to be in contactwith the inner surface of the flat pipe, and projection portions whichproject from both flat plate portions toward the opposing flat plateportion and the opposing tops of which are made come into contact witheach other.

Accordingly, in thus constitution, because two opposing flat plateportions are in contact with the inner surface of the flat pipe, it ispossible to increase the stiffness to the width directional force of theinner fin itself and the contact resistance to the width directionalforce at the contact portion between the inner fin and the flat pipe,and further because the tops of the projection portions which areprojected from one of the both flat plates to the opposing flat plateare in contact with one anther, it is possible to increase the stiffnessto the binding force by the flat pipe in the thickness direction, as aresult, it is possible to prevent the disadvantage such that significantdeformation of the inner fin is occurred at the time of cutting the flatpipe.

The projection portions may be constituted of folded portions which arefolded so as to abut, and the tops of them may be formed flatly.Besides, a cross sectional shape of the projection portion may be formedso as to focus against the top portion thereof.

The above mentioned tube has a constitution available to a case offorming by involving the inner fin in the flat pipe at the time offorming the plate pipe and making the flat plates of it be in contactwith inner surface of the flat pipe, and cutting the flat pipe with theinner fin.

Besides, it is preferred when a saving-thickness of the tube is designedthat the above mentioned flat pipe and inner fin are bonded by a brazingmaterial cladded on the inner fin. Furthermore, it is preferred whencorrosion proof of the tube is increased that a sacrificial erosionlayer is cladded on an outer surface of the flat pipe. Moreover, it ispreferred when flow resistance of the flow path is decreased that theinner fin is formed thinner than thickness of the flat pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a constitutional example of a heat exchanger usingtubes according to the present invention, (a) is a front view thereof,and (b) is a side view shown from a side on which an intake and outletof coolant are provided.

FIG. 2 is a diagram showing each part of the heat exchanger shown inFIG. 1, FIG. 2 (a) is a cross sectional view cut by a I—I line in FIG. 1(a), FIG. 2 (b) is a cross sectional view cut by a II—II line in FIG. 1(a), and FIG. 2 (c) is a cross sectional view cut by a III—III line inFIG. 1 (b).

FIG. 3 (a) is a cross sectional view showing a tube structure examplewhich is constituted by involving the inner fin to the flat pipe beforecutting, and FIG. 3 (b) is a cross sectional view showing an inner finused in the tube in FIG. 3 (a).

FIG. 4 is a diagram showing a forming process of a flat tube.

FIG. 5 (a) is a cross sectional view showing an improved example of FIG.3 (a) and showing a tube before cutting, and FIG. 5 (b) is a crosssectional view showing an inner fin using in the tube in FIG. 5 (a).

FIG. 6 (a) is a cross sectional view showing another tube structureexample constituted by involving an inner fin in the flat pipe, and FIG.6 (b) is a cross sectional view showing an inner fin used in the tube inFIG. 6 (a).

FIG. 7 is a diagram showing an improved example of FIG. 6 (a), FIG. 7(a) is a diagram showing a condition that a gap α is formed between afolded portion 16 c of the flat pipe and a connecting portion 17 a, FIG.7 (b) is a diagram showing an example that a side of a connected tab 16d of the flat pipe faces to a connecting portion 17 a and the connectedtab 16 d is in contact with the connecting portion 17 a, and FIG. 7 (c)is a diagram showing an example that a side of a connected tab 16 d ofthe flat pipe faces to a connecting portion 17 a and a gap β is formedbetween the connected tab 16 d and the connecting portion 17 a.

FIG. 8 (a) is a cross sectional view illustrating a tube before cuttingshowing an improved example of FIG. 6 (a), and FIG. 8 (b) is a crosssectional view showing an inner fin used in the tube in FIG. 8 (a).

FIG. 9 (a) is a cross sectional view illustrating an another tubestructure example before cutting which is constituted by involving aninner fin into the flat pipe, and FIG. 9 (b) is a cross sectional viewshowing the inner fin used in the tube.

FIG. 10 is a diagram illustrating a method such as to cut the priorforming tube by a cutting blade C.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a working mode of the present invention is explained due todrawings. In FIGS. 1 and 2, a heat exchanger 1 is, for instance, to beused as an evaporator constituting a part of a refrigerating cycle, andprovided with a pair of tanks 2, 3, a plurality of flat tubes 4communicating between the pair of tanks 2, 3, corrugated fins 5 insertedand connected between the tubes 4 and an intake 6 and outlet 7 ofcoolant, and constituted by having a side tank 8 communicating with thetank.

Hereinafter explaining about one of the tanks 3 because the tanks 2, 3are located so as to face to each other with a specific distance andthey have a basically similar structure except for a structure in middleportions thereof. The tank 3 is, as shown in FIG. 2 (b), constituted ofan end plate 11 in that tube insertion holes 10 in each of which anopening end portion 4 a of the flat tube 4 is inserted and connected areformed, a tank plate 12 engaging with the end plate 11 and constitutinga cylindrical body together with the end plate 11, and caps 13 whichblockades opening end portions of the cylindrical body constituted ofthe end plate 11 and the tank plate 12. An inner portion of the tank 3is divided to tank spaces 3 a, 3 b in front and behind in a ventilationdirection (a width direction) by a partition plate 11 which is formedunitedly to the end plate 11 and extends in a laminating direction.

Besides, the inner portions of the tanks 2, 3 are divided at specificpositions in the laminating direction according to a number of passes ofheat exchanging medium. In this embodiment, the lower tank 3 is dividedin a middle of the laminating direction and a cap 14 is arranged in thedivided portion, so that four-pass type heat exchanger that the heatexchanging medium is flown four times between the tanks as a whole isconstituted.

The side tank 8 is formed together with an inflow passage 8 a and anoutflow passage 8 b unitedly by extrusion and connected with each of theend plate 11 of the tanks 2, 3. The inflow passage 8 a is connected witha tank portion locating at an upper stream side and the outflow passage8 b is connected with a tank portion located at a downstream sideaccording to the number of passes. In the four-pass type heat exchangershown in this embodiment, the inflow passage 8 a is communicated withone tank space 3 a of the tank 3 and the outflow passage 8 b iscommunicated with another tank space 3 b of the tank 3.

Accordingly, coolant transferred from an expansion valve not shown infigures is flown into an upper stream portion of the tank 3 via the sidetank 8 and moved between the tanks 2, 3 via the flat tubes 4, exchangingheat with an air passing through the fins 5 in this process. And then,the coolant is flown out of a downstream portion of the tank 3 via theside tank 8 finally.

Each of the flat tube 4 is that both ends inserted into the tanks 2, 3is opened, as shown in FIG. 3, and is constituted by housing an innerfin 17 in a flat pipe 16 in which a path 15 for heat exchanging mediumis formed. The flat pipe 16 is formed by a roll forming from a sheet ofa material for flat pipe constituted by a metal with good heatconduction such as aluminum, wherein flat portions 16 a, 16 b facingeach other are formed. In this embodiment, the material for flat pipe isdoubled in an axis along a longitudinal direction thereof, a bendingportion 16 c is formed at one end in a width direction thereof, and aconnected tab 16 d is formed at another end in the width direction.

The inner fin 17 included in the flat pipe 16 is constituted of aconnecting portion 17 a formed along one of side edges of the flat pipe16, both flat plate portions 17 b, 17 c formed in a flat shape andfacing each other which are connected each other via the connectingportion 17 a and are in contact with inner surfaces of the flat portions16 a, 16 b, projection portions 17 d each of which is projected from oneof the flat plate portions 17 b, 17 c to the other of the flat plateportions 17 b, 17 c and whose tops are in contact with an inner surfaceof the opposing flat plate portion.

In this embodiment, each of the flat plate portions 17 b, 17 c is formedin the approximately same width as the path 15, and each of theprojection portions 17 d is constituted of a folded portion which isfolded so as to come into contact. The projection portions 17 d areformed in plural at specific intervals in both flat plate portions 17 b,17 c, wherein each of tops is in contact with an inner surface (anopposite surface to a side which the inner surface of the flat pipe 16is in contact with) of the opposite flat plate portion 17 b, 17 c, sothat the path 15 in the flat pipe is divided into a plurality of smallflow paths 15 a whose equivalent diameters are small.

Besides, the inner fin 17 used here is that brazing material is cladedon both sides thereof and the inner fin 17 is set thinner than thicknessof the flat pipe 16. Furthermore, a sacrificial layer is provided on anouter surface of the flat pipe 16 in order to increase a corrosionproof. Note that it is possible that the inner fin is made of a barematerial owing to using capillarity arising at the time of meltingbrazing material of the tank.

The flat tube 4 formed thus is, as shown in a forming process example inFIG. 4, formed by involving the inner fin 17 shown in FIG. 3 (b) whichis formed another process so as to cover the inner fin 17 with thematerial for flat pipe on the way of the process for forming the flatpipe 16 by the roll forming, namely in the process for forming in a tubeshape by folding so as to roll up the material for flat pipe, andcutting the flat pipe 16 together with the inner fin 17 at a specificlength. Then, the cut flat pipes 16 are installed to the tube insertionholes 10 of the tanks 2, 3 and the fins are inserted between the tubesto assemble as a heat exchanger, and the assembled heat exchanger isfixed by jigs as a whole and inserted into a furnace, so that theconnected tabs 16 d of the plat pipe 16 are brazed and the inner fins 17are brazed on inner surfaces of the flat pipes 16 by brazing materialscladed on the inner fins 17 themselves, respectively.

In the above mentioned structure, in the cutting process before brazing,though the tubes are in a condition such as to be held from outsidethereof and force is applied to the inner fin 17 in a width direction ofthe tube 4 by inserting the cutting blade, the stiffness to the force inthe width direction of the inner fin itself can be increased becauseeach of the inner fins has two flat plate portions 17 b, 17 c opposingeach other which are connected via the connecting portion 17 a, and itis possible that contact resistance at contact portions between theinner fin 17 and the flat pipe 16 becomes large because the flat plateportions 17 b, 17 c are in contact with the inner surface of the flatpipe 16 in a surface contact. Moreover, because each top of theprojection portions 17 d formed on each of the flat plate portions 17 b,17 c comes in contact with the inner surface of the opposite flat plateportion, stiffness in a thickness direction of the flat pipe 16 can beincreased. Therefore, disadvantage that the inner fin 17 is deformedextremely so as to shift the inner fin 17 largely in the width directioncan be decreased and it is possible to secure a plurality of the smallflow paths 15 a whose equivalent diameters are small in the flat pipe.

Another embodiment of the inner fin 17 included in the above flat pipe16 is shown in FIG. 5. This inner fin 17 is constituted so that theprojection portions 17 d are formed only in one of the flat plateportions 17 b, another of the flat plate portions 17 c is constituted ofa continuous flat surface in contact with the flat portion 16 b of theflat pipe 16, and the top of each projection portion 17 d is in contactwith the inner surface (a opposite surface to the side which the innersurface of the flat pipe 16 is in contact with) of the flat plateportion 17 c. The projection portions 17 d used in this embodiment areformed in the flat plate portion 17 b at a specific pitch which is anapproximately half pitch in the projection portions 17 d formed in theflat plate portions 17 b, 17 c in the aforementioned structure so as tomake an equivalent diameter of the small flow path 15 a approximatelysimilar to the aforementioned structure example.

Also in thus structure, two flat plate portions 17 b, 17 c facing eachother and connected via the connecting portion 17 a are in contact withthe inner surface of the flat pipe 16 by a surface contact, so that thestiffness to the force in the width direction of the inner fin itselfcan be increased and the contact resistance at the contact portionbetween the inner fin 17 and the flat pipe 16 can be enlarged.Accordingly, also in this embodiment, disadvantage that the inner fin 17is deformed extremely so as to shift the inner fin 17 largely in thewidth direction can be decreased and it is possible to secure aplurality of the small flow paths 15 a whose equivalent diameters aresmall in the flat pipe.

The other structure example of the inner fin 17 included in theaforementioned flat pipe 16 is shown in FIG. 6. In this inner fin 17,each of the projection portions 17 d is formed in a trapezoidal shape ina cross sectional view by a top portion 17 d-1 formed flatly andconstructing portions 17 d-2 constructing between the top portion 17 d-1and the flat plate portion (17 b or 17 c). In this embodiment, theprojection portions are formed in both of the flat plate portions 17 b,17 c in plural at specific intervals, and each top of them is in contactwith the inner surface (a opposite surface to the side which the innersurface of the flat pipe 16 is in contact with) of the flat plateportion opposing thereto so as to divide the flow path 15 to a pluralityof small flow paths 15 a whose equivalent diameters are small. Note thatthe other components are similar to ones of the aforementioned structureexamples, so that the explanation is omitted by marking the samereference number to the same parts respectively.

In thus structure, two flat plate portions 17 b, 17 c facing each otherand connected via the connecting portion 17 a are in contact with theinner surface of the flat pipe 16 by a surface contact, so that thestiffness to the force in the width direction of the inner fin itselfcan be increased and the contact resistance at the contact portionbetween the inner fin 17 and the flat pipe 16 can be enlarged.Furthermore, because the tops 17 d-1 of the projection portions 17 d areformed in a flat shape and are in contact with the inner surface of theopposite flat plate portion, the contact resistance between theprojection portions 17 d and the flat plate portions 17 b, 17 c can beenlarged, and the stiffness to the force in the thickness direction ofthe flat pipe can be increased. Accordingly, disadvantage that the innerfin 17 is deformed extremely so as to shift the inner fin 17 largely inthe width direction can be decreased and it is possible to secure aplurality of the small flow paths 15 a whose equivalent diameters aresmall in the flat pipe. Besides, in the aforementioned shape, thecontact resistance is large at a contact portion between each of theprojection portions of the inner fin and the flat portion, so thatcutting that deformation is small can be achieved even if the connectingportion of the inner fin is not in contact with the inner surface of theflat pipe.

Besides, the aforementioned constructing portion 17 d-2 is preferredthat an angle of inclination thereof to the flat plate portion 17 b, 17c is set within a range of 45°–90° since cutting of inner fin 17 isfacilitated and it is necessary to secure the equivalent path with asmall equivalent diameter, the aforementioned constructing portion 17d-2, and the equivalent diameter of each small flow path 15 a defined bythe inner fin 17 is set within a range of 0.7 mm–1.5 mm when height ofthe tube is set within a range of 1.5 mm–2.3 mm, thickness of the flatpipe is set within a range of 0.15 mm–0.25 mm, and plate thickness ofthe inner fin is set within a range of 0.06 mm–0.13 mm. According tosetting the angle of inclination in the constructing portions 17 d-2within the above range, the stiffness of the constructing portions 17d-2 of the inner fin 17 is secured, so that the cutting by the cuttingblade becomes easy.

Moreover, in the aforementioned structure, improvement as shown in FIG.7 may be adopted. Namely, though the structure shown in FIG. 6 is that afolding portion 16 c in the flat pipe 16 of the tube 4 is in contactwith the connecting portion 17 a of the inner fins 17, a gap (a) may beformed between the folding portion 16 c and the connecting portion 17 aso as to form a play between them. It is confirmed that bad brazing inthe inner fin is hard to occur rather than the above structure examplethat the folding portion 16 c is in contact with the connecting portion17 a.

Furthermore, in the aforementioned structure, the inner fin 17 is housedin the flat pipe 16 so as to oppose the folding portion 16 c of the flatpipe 16 to the connecting portion 17 a of the inner fin 17, but theinner fin 17 may be housed so as to oppose the connected tab 16 d of theflat pipe 16 to the connecting portion 17 a of the inner fin 17 byreversing the inner fin 17. Namely, the inner fin 17 may be housed sothat the connecting portion 17 a comes in contact with the connected tab16 d, or so that a gap (β) is formed between the connected tab 16 d andthe connecting portion 17 a to form a play between them. In thusstructure, it is confirmed that bad brazing in the inner fin is hard tooccur.

FIG. 8 shows the other improvement of the inner fin 17 shown in FIG. 6which is included in the flat pipe 16. In this inner fin 17, theprojection portion 17 d has a cross-sectional shape so as to focusagainst a top thereof, namely is formed in a triangle shape in a crosssection such that tops of both constructing portions 17 d-3 inclining tothe flat plate portions are abutted each other in this example. Thusprojection portions 17 d are also formed in both flat plate portions 17b, 17 c in plural at a specific intervals, and each top of them is incontact with the inner surface (a opposite surface to the side which theinner surface of the flat pipe 16 is in contact with) of the flat plateportion opposing thereto so as to divide the flow path 15 to a pluralityof small flow paths 15 a whose equivalent diameters are small. Note thatthe other components are similar to ones of the aforementioned structureexamples, so that the explanation is omitted by marking the samereference number to the same parts respectively.

Accordingly, also in this example, two flat plate portions 17 b, 17 cfacing each other and connected via the connecting portion 17 a are incontact with the inner surface of the flat pipe 16 by a surface contact,so that the stiffness to the force in the width direction of the innerfin itself can be increased and the contact resistance at the contactportion between the inner fin 17 and the flat pipe 16 can be enlarged.Because the tops of the projection portions 17 d are in contact with theinner surface of the opposite flat plate portion, the stiffness to theforce in the thickness direction of the flat pipe can be increased.Therefore, disadvantage that the inner fin 17 is deformed extremely soas to shift the inner fin 17 largely in the width direction can bedecreased and it is possible to secure a plurality of the small flowpaths 15 a whose equivalent diameters are small in the flat pipe.

Another improvement of the inner fin 17 is shown in FIG. 9. In thisinner fin 17, projection portions 17 d are formed from both flat plateportions 17 b, 17 c to the opposite flat plate portions respectively andthe tops of the projection portions 17 d are in contact with the topsopposite thereto. In this embodiment, the projection portions 17 d areformed by folding portions which are folded so as to be in contact withone another and the tops which face one another are in contact with oneanother, so that the flow path 15 is divided to a plurality of smallflow paths 15 a with small equivalent diameters respectively. Note thatthe other components are similar to ones of the aforementioned structureexamples, so that the explanation is omitted by marking the samereference number to the same parts respectively.

Accordingly, in thus structure, two flat plate portions 17 b, 17 cfacing each other and connected via the connecting portion 17 a are incontact with the inner surface of the flat pipe 16 by a surface contact,so that the stiffness to the force in the width direction of the innerfin itself can be increased and the contact resistance at the contactportion between the inner fin 17 and the flat pipe 16 can be enlarged.Because the tops of the projection portions 17 d are in contact with theinner surface of the opposite flat plate portion, the stiffness to theforce in the thickness direction of the flat pipe can be increased.Therefore, disadvantage that the inner fin 17 is deformed extremely soas to shift the inner fin 17 largely in the width direction can bedecreased and it is possible to secure a plurality of the small flowpaths 15 a whose equivalent diameters are small in the flat pipe.

Besides, in the structure shown in FIG. 9, though the example thatabutted projection portions are constituted of the folding portions isshown, if the small flow paths with available equivalent diameters canbe formed, each projection portion may be made in the approximatelytrapezoidal shape in a cross section as shown in FIG. 6, or may be madein the approximately triangle shape in a cross section as shown in FIG.8, and further the tops which face one another may be abutted.

INDUSTRIAL APPLICABILITY

As above mentioned, according to this invention, because an inner finarranged in a flow path of a flat pipe is constituted of two oppositeflat plate portions formed in a flat plate shape so as to be connectedalong one of side edges of the flat pipe and be in contact with an innersurface of the flat plate portion, and projection portions which projectfrom at least one of the flat plate portions and whose tops are incontact with another of the opposite flat plate portions, or constitutedof two opposite flat plate portions formed in a flat plate shape so asto be connected along one of side edges of the flat pipe and be incontact with an inner surface of the flat plate portion, and projectionportions which project from both of the flat plate portions and whosetops are in contact with one another, stiffness to a force in a widthdirection of the inner fin, the contact resistance to the force in thewidth direction at a contact portion between the inner fin and the flatpipe, and further stiffness to restricting force in a thicknessdirection by the flat pipe can be increased, as a result, in the case ofcutting the flat pipe in the condition that the inner fin is included,it is possible to be hard to shift the inner fin and it is possible tosecure a plurality of paths, whose equivalent diameters are small, inthe flat pipe.

1. A tube for a heat exchanger constituted of a flat pipe whose bothends are opened and in which a flow path for a heat exchanging mediumand an inner fin arranged in said flow path of the flat pipe and formedseparately from said flat pipe thinner than a thickness of said flatpipe, wherein said flat pipe is constituted by a sheet of material for aflat pipe, characterized in that: said inner fin is constituted of twoopposing flat plate portions connected along one of side edges of saidflat pipe and formed in a flat plate shape so as to be in contact withan inner surface of said flat pipe, and projection portions which areprojected from at least one of the flat plate portions and whose topsare in contact with the other opposing flat plate portion, and said tubeis formed by cutting said flat pipe together with said inner fin.
 2. Atube for a heat exchanger according to claim 1, characterized in thateach top of said projection portions is formed flatly.
 3. A tube for aheat exchanger according to claim 1, characterized in that each of saidprojection portions has a shape in a cross section such as to focusagainst the top thereof.
 4. A tube for a heat exchanger according toclaim 1, 2 or 3, characterized in that said flat pipe and said inner finare brazed by a brazing material cladded on said inner fin.